scripts.js

    function getRandomColor() {
        var letters = '0123456789ABCDEF'.split('');
        var color = '#';
        for (var i = 0; i < 6; i++ ) {
            color += letters[Math.floor(Math.random() * 16)];
        }
        return color;
    }

    //alert(getRandomColor());

    var clickedTime; var createdTime; var reactionTime;

    function makeBox(){     

        var time = Math.random();

        time = 2000 * time;

        setTimeout(function(){

            if(Math.random()>0.5){

                document.getElementById("box").style.borderRadius = "100px";

            }else{
                document.getElementById("box").style.borderRadius = "0";
            }

            var top=Math.random();

            top= top*300;

            var left=Math.random();

            left= left*500;

            document.getElementById("box").style.top=top+"px";

            document.getElementById("box").style.left=left+"px";

            document.getElementById("box").style.backgroundColor=getRandomColor();

            document.getElementById("box").style.display="block";

            createdTime = Date.now();
        }, time);

    }

    document.getElementById("box").onclick=function(){
        //document.getElementById("box").style.display="none";

        clickedTime = Date.now();

        reactionTime = (clickedTime - createdTime)/1000;

        document.getElementById("time").innerHTML = reactionTime;    

        this.style.display="none";
        makeBox();
    }

    makeBox();